Tracker With Switchable Radiation Characteristics

ABSTRACT

A tracker, a surgical navigation system with the tracker, and a method of operating the tracker are described. The tracker comprises a first switch configured to be operated between a first switch configuration and a second switch configuration. The tracker also comprises one or more sources of electromagnetic radiation configured to selectively emit electromagnetic radiation with a first radiation characteristic or a second radiation characteristic. The tracker further comprises electrical circuitry configured to selectively control the one or more sources of electromagnetic radiation to emit electromagnetic radiation having the first radiation characteristic in the first switch configuration and to emit electromagnetic radiation having the second radiation characteristic in the second switch configuration, wherein the second radiation characteristic is different from the first radiation characteristic.

PRIORITY CLAIM

This application claims priority under 35 U.S.C. § 119 to EuropeanPatent Application No. 20213089.4, filed Dec. 10, 2020, the entirecontents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure generally relates to tracker, for example in thecontext of surgical navigation. In particular, a tracker with switchableradiation characteristics, a surgical navigation system comprising thetracker, and a method of operating the tracker are presented.

BACKGROUND

Surgical navigation systems are typically configured to track surgicalobjects such as a surgical instrument or a patient. A common trackingtechnique involves a tracker with a source of electromagnetic radiationas well as an optical sensor capable of detecting the electromagneticradiation emitted by the tracker. Based on the detected electromagneticradiation, information on one or both of a position and an orientationof the tracker can be determined.

During a surgical procedure, the surgeon may want to communicate withthe surgical navigation system, but typical user interfaces such as akeyboard and a mouse may be arranged at an inconvenient distance orinconvenient place. Moreover, such user interfaces pose a contaminationrisk for a sterile surgery environment. Especially communication withthe surgical navigation system for calibrating or operating the trackermay be time consuming and result in contamination of the sterile surgeryenvironment.

The surgeon may disinfect his or her hands after having operated theuser interface. However, such disinfecting procedures are timeinefficient and strenuous.

SUMMARY

There is a need for a technique that solves one or more of theaforementioned or other problems.

According to a first aspect, a tracker for a surgical navigation systemis provided. The tracker comprises a first switch configured to beoperated between a first switch configuration and a second switchconfiguration. The tracker comprises one or more sources ofelectromagnetic radiation configured to selectively emit electromagneticradiation with a first radiation characteristic or a second radiationcharacteristic. The tracker further comprises electrical circuitryconfigured to selectively control the one or more sources ofelectromagnetic radiation to emit electromagnetic radiation having thefirst radiation characteristic in the first switch configuration and toemit electromagnetic radiation having the second radiationcharacteristic in the second switch configuration, wherein the secondradiation characteristic is different from the first radiationcharacteristic.

The first switch may be configured to be operated while the tracker isbeing tracked by the surgical navigation system. The first switch may beconfigured to be operated upon configuring (e.g., assembling) thetracker in preparation of a surgical procedure. The first switch may beuser-operable.

The first switch, or any further switch, may be configured to beoperated between more than two switch configurations, such as three,four, five, six, or more switch configurations. In such a case, one ofthe switch configurations may be configured to switch off the tracker(e.g., to switch off a power source integrated into the tracker).

The source of electromagnetic radiation may be configured to emitelectromagnetic radiation with more than two radiation characteristics,such as two, three, four, five, or more radiation characteristics.

The source of electromagnetic radiation may be a light emitting diode(LED), a polymer light emitting diode, a laser, an incandescent lightbulb, or a fibre cable (e.g., an end face or side face thereof) coupledto a light source. The source of electromagnetic radiation may beconfigured to emit electromagnetic radiation in at least one of thevisible light spectrum, the infrared light spectrum, and the ultravioletlight spectrum.

The first radiation characteristic may comprise emission ofelectromagnetic radiation at a first operation frequency and the secondradiation characteristic may comprise emission of electromagneticradiation at a second operation frequency different from the firstoperation frequency. The first and second operation frequencies may eachindicate a rate of a periodic intensity change of the electromagneticradiation. The intensity of the electromagnetic radiation may changebetween a first intensity and a second intensity that is smaller thanthe first intensity. The second intensity may be zero or essentiallyzero. One of the first operation frequency and the second operationfrequency may be zero with a continuous emission of electromagneticradiation.

The first radiation characteristic may comprise emission ofelectromagnetic radiation having a first wavelength and the secondradiation characteristic may comprise emission of electromagneticradiation having a second wavelength different from the firstwavelength. The first and second wavelengths may be in a visible lightspectrum. Alternatively, the first and second wavelengths may be in aninfrared light spectrum. Further alternatively, one of the first andsecond wavelengths may be in the visible light spectrum and the otherone of the first and second wavelengths may be in the infrared lightspectrum.

The tracker may comprise a plurality of sources of electromagneticradiation, such as two, three, four, five, or more sources ofelectromagnetic radiation. In such a case, changing between the firstand second radiation characteristics of the plurality of sources ofelectromagnetic radiation may comprise at least one of (i) at least oneof the sources of electromagnetic radiation starting emittingelectromagnetic radiation and (ii) at least one of the sources ofelectromagnetic radiation stopping emitting electromagnetic radiation. Afirst subset of sources of electromagnetic radiation may compriseexactly two sources of electromagnetic radiation. In someimplementations, in the first radiation characteristic only one sourceof the first subset is configured to emit electromagnetic radiation, andin the second radiation characteristic only the other source of thefirst subset is configured to emit electromagnetic radiation.

In case the tracker comprises a plurality of sources of electromagneticradiation as described above, a second switch may be configured to beoperated between a third switch configuration and a fourth switchconfiguration. A, or the, first subset of the plurality of sources ofelectromagnetic radiation may be assigned to the first switch, and asecond subset of the plurality of sources of electromagnetic radiationmay be assigned to the second switch. The first subset of the pluralityof sources of electromagnetic radiation may be configured to selectivelyemit electromagnetic radiation having a first partial radiationcharacteristic or a second partial radiation characteristic. The secondsubset of the plurality of sources of electromagnetic radiation may beconfigured to selectively emit electromagnetic radiation having a thirdpartial radiation characteristic or a fourth partial radiationcharacteristic. The first and second switches may be configured to beoperated to only change the partial radiation characteristic of eachassigned subset of sources of electromagnetic radiation.

The tracker may comprise an indicator configured to provide a firstindication in the first switch configuration and a second indication inthe second switch configuration. The first and second indications may beat least one of optically and haptically distinguishable for a user. Theone or more sources of electromagnetic radiation may in particular beconfigured to emit infrared radiation. The indicator may comprise anindicator light source configured to emit visible light perceivable bythe human eye. The indicator may comprise a switch position indicatorconfigured to assign a first position of the first switch to the firstswitch configuration and to assign a second position of the first switchto the second switch configuration.

The first switch may be pre-configured to assume the first switchconfiguration and adapted to switch from the first to the second switchconfiguration only for a duration that the first switch is operated orfor a fixed time duration after the first switch was operated. The firstswitch may be a spring-biased switch (e.g., a push button switch).

The tracker may comprise at least one powering component configured toprovide power to the one or more sources of electromagnetic radiation,such as a power source (e.g., one or more button cell batteries) and/ora wireless power reception device. The power source may comprise two,three, four, or more button cell batteries. The power source maycomprise a CR2032 and/or a CR2025 type button cell battery.

The tracker may comprise one or more passive tracking elementsconfigured to reflect electromagnetic radiation. The tracker maycomprise two, three, four, five, six, or more passive tracking elements.The one or more passive tracking elements may be configured to reflectpredominantly visible light or infrared light. The one or more passivetracking elements may comprise reflective spheres.

The tracker may have more than two switch configurations. In somevariants, the one or more sources of electromagnetic radiation may beconfigured to selectively emit electromagnetic radiation with a numberof radiation characteristics at least equal to the number of switchconfigurations, wherein each of the switch configurations may beassigned to one of the radiation characteristics. For example, thetracker may have three switch configurations each assigned to one ofthree radiation characteristics, or the tracker may have four switchconfigurations each assigned to one of four radiation characteristics.

The first switch (and/or, optionally, a second switch) may comprise amechanical switch configured to be operated by a user (e.g., while thetracker is being tracked). The mechanical switch may comprise one ormore elements movable by the user to change the switch configuration.The switch may comprise a push button. The switch may comprise a slidingportion configured to be slid parallel to a tracker surface.

The first switch may comprise a first switch portion, a second switchportion configured to be electrically coupled to the first switchportion, and a third switch portion configured to be electricallycoupled to the first switch portion. In some variants, the first switchis in the first switch configuration when the second switch portion iselectrically coupled to the first switch portion and in the secondswitch configuration when the third switch portion is electricallycoupled to the first switch portion.

The tracker may comprise a first tracker part and at least one secondtracker part that is at least one of movable relative to and removablefrom the first tracker part, wherein the first switch portion isprovided at the first tracker part and the second switch portion and thethird switch portion are collectively or individually provided at the atleast one second tracker part. As an example, the second switch portionmay be provided at one second tracker part and the third switch portionmay be provided at another second tracker part. Alternatively, both thesecond and third switch portion may be provided at a single secondtracker part. The first tracker part and a dedicated second tracker partmay be configured to selectively assume a first relative position torealize the first switch configuration and a second relative position torealize the second switch configuration. The different relativepositions may be defined by one or both of rotatory relative positionsand translatory relative positions.

One of the first and the at least one second tracker part may carry theone or more sources of electromagnetic radiation. The other of the firstand the at least one second tracker part may comprise an interface forcoupling the tracker to an object that is to be tracked.

According to a second aspect, a surgical navigation system is provided.The surgical navigation system comprises the tracker described hereinand an optical sensor capable of detecting different radiationcharacteristics of the tracker. The surgical navigation system furthercomprises a processor configured to selectively identify the first orsecond switch configuration based on the radiation characteristicdetected by the optical sensor.

The processor may be configured to selectively identify the first orsecond switch configuration based on a comparison between the detectedradiation characteristic and a predetermined radiation characteristic.

The processor may be configured to assign a first tracking mode to thefirst switch configuration and a second tracking mode to the secondswitch configuration. The first and/or second tracking modes may beassigned to an instrument and/or a patient. The first and/or secondtracking modes may be assigned to different body parts of the patient.

The processor may be configured to identify a switching between thefirst and second switch configuration. The processor may be configuredto determine a command issued by a user based on the identifiedswitching between the first and second switch configuration. Theprocessor may be configured to control a navigation procedure based onthe command thus determined.

The optical sensor may be a camera, such as a mono camera or a stereocamera. In the case that the first radiation characteristic comprisesemission of electromagnetic radiation at a first operation frequency andthe second radiation characteristic comprises emission ofelectromagnetic radiation at a second operation frequency different fromthe first operation frequency as described above, the optical sensor maybe a camera having a frame rate that is at least two times larger than alarger one of the first and second operation frequencies of the tracker.

In the case that the tracker comprises one or more passive trackingelements configured to reflect electromagnetic radiation, the opticalsensor may be configured to detect electromagnetic radiation reflectedby the one or more passive tracking elements.

According to a third aspect, a method for operating a tracker for asurgical navigation system is provided. The tracker comprises a firstswitch configured to be operated between a first switch configurationand a second switch configuration, one or more sources ofelectromagnetic radiation, electrical circuitry configured toselectively control the one or more sources of electromagnetic radiationto emit electromagnetic radiation with a first radiation characteristicor a second radiation characteristic, wherein the second radiationcharacteristic is different from the first radiation characteristic. Themethod may comprise providing power to the one or more sources ofelectromagnetic radiation. The method further comprises emitting, by theone or more sources of electromagnetic radiation, electromagneticradiation having the first radiation characteristic in the first switchconfiguration and electromagnetic radiation having the second radiationcharacteristic in the second switch configuration.

According to a fourth aspect, a computer program product is provided,wherein the computer program product comprises program code portionsconfigured to perform the method described herein when executed by aprocessor. The computer program product may be stored on acomputer-readable recording medium. The computer-readable recordingmedium may be a non-transitory recording medium, such as a hard drive,USB stick, or a compact disc.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, advantages and aspects of the present disclosure willbecome apparent from the following embodiments taken in conjunction withthe drawings, wherein:

FIG. 1 shows an embodiment of a surgical navigation system comprising aprocessor, an optical sensor, and a tracker;

FIG. 2A shows a perspective view of an embodiment of a tracker in afirst switch configuration;

FIG. 2B shows a perspective view of the tracker shown in FIG. 2A in asecond switch configuration;

FIG. 3A shows an embodiment of a tracker with three passive trackingelements in a first switch configuration;

FIG. 3B shows the tracker of FIG. 3A in a second switch configuration;

FIG. 4A shows an embodiment of tracker with a first switch thatcomprises a first, second, and third switch portion;

FIG. 4B shows the first switch portion electrically coupled to thesecond switch portion;

FIG. 4C shows the first switch portion electrically coupled to the thirdswitch portion;

FIG. 5 shows a flowchart of an embodiment of a method for operating thetracker described herein;

FIG. 6A shows a tracker with three switch configurations each assignedone of three radiation characteristics, wherein the switch is in a firstof three switch configurations;

FIG. 6B shows the tracker shown in FIG. 6A wherein the first switch isin a second of three switch configurations;

FIG. 6C shows the tracker shown in FIG. 6A wherein the first switch isin a third of three switch configurations;

FIG. 6D shows a tracker with three switch configurations, wherein thefirst switch is in a first switch configuration assigned to a firstradiation characteristic;

FIG. 6E shows the tracker shown in FIG. 6D, wherein the first switch isin a second switch configuration assigned to a second radiationcharacteristic;

FIG. 6F shows the tracker shown in FIG. 6D, wherein the first switch isa third switch configuration configured to turn off the tracker;

FIG. 7A shows an embodiment of a tracker with a plurality of indicatorsproviding a first indication in a first switch configuration;

FIG. 7B shows the tracker shown in FIG. 7A with the plurality ofindicators providing a second indication in a second switchconfiguration;

FIG. 8A shows an intensity of the electromagnetic radiation of a firstoperation frequency;

FIG. 8B shows an intensity of the electromagnetic radiation of a firstoperation frequency, wherein the intensity alternates between anintensity of zero and an intensity that is larger than zero;

FIG. 8C shows a change of the intensity of the electromagnetic radiationfrom a first operation frequency to a second operation frequency;

FIG. 8D shows a first change of the intensity of the electromagneticradiation from a first operation frequency to a second operationfrequency followed by a second change of the intensity back to the firstoperation frequency;

FIG. 8E shows an intensity of electromagnetic radiation during acontinuous emission;

FIG. 9A shows an embodiment of a tracker with a plurality of sources ofelectromagnetic radiation

FIG. 9B shows the tracker shown in FIG. 9A wherein the sources ofelectromagnetic radiation stop, continue, or start emittingelectromagnetic radiation;

FIG. 10A shows another embodiment of a tracker, wherein three out ofeight sources of electromagnetic radiation emit electromagneticradiation;

FIG. 10B shows the tracker shown in FIG. 10A, wherein all sources ofelectromagnetic radiation emit electromagnetic radiation;

FIG. 11A shows an embodiment of a tracker with a first switch and asecond switch emitting a first radiation characteristic;

FIG. 11B shows the tracker shown in FIG. 11A emitting a second radiationcharacteristic;

FIG. 11C shows the tracker shown in FIG. 11A emitting a third radiationcharacteristic;

FIG. 11D shows the tracker shown in FIG. 11A emitting a fourth radiationcharacteristic;

FIG. 12A shows an embodiment of a tracker with four subsets of sourcesof electromagnetic radiation and four switches; and

FIG. 12B shows an embodiment of a tracker with four subsets each withfour of sources of electromagnetic radiation.

DETAILED DESCRIPTION

The tracker described herein may be used for any tracking technologyinvolving emission of electromagnetic radiation, such as motion capturetechnology and tracking of virtual reality headsets. In the following,the tracker is described in the context of a surgical navigation system,but it should be understood that the tracker is not limited thereto.

FIG. 1 schematically shows a surgical navigation system 10 comprising aprocessor 12, an optical sensor 14, and a tracker 16. The processor 12is provided by a computer system 18. Alternatively, the processor 12 maybe provided by a remote server or cloud computing resources.

The optical sensor 14 may be or may comprise a camera. The opticalsensor 14 is configured to detect visible light and infrared light.Alternatively, the optical sensor 14 may be configured to detect atleast one or any combination of at least one of visible light, infraredlight, and ultraviolet light.

The tracker 16 comprises a mechanical interface for being coupled to asurgical object. The tracker 16 shown in FIG. 1 is coupled to a surgicalobject 20 in form of a skin area around a tibia of a patient.Alternatively the tracker 16 may be coupled to other regions of thepatient, such as directly to the bone (e.g., the tibia) or an externalelement coupled to the patient (e.g., a table the patient is arrangedon).

FIG. 2A shows a perspective view of the tracker 16 in a schematicrepresentation. The tracker 16 comprises at least one source 22 ofelectromagnetic radiation. For example, a single source 22 ofelectromagnetic radiation may be used for tracking a surgical instrumentwith only two freedoms of movement. In another realization, a pluralityof trackers 16 each with a single source 22 of electromagnetic radiationmay be individually coupled to a plurality of vertebra of the patient inorder to track deformation of the spine. In other embodiments, thetracker may comprise a plurality of sources 22 of electromagneticradiation, such as two, three, four or more. The tracker 16 may inparticular comprise three or four (or more) such sources 22 so that thenavigation system 10 can determine one or both of a position and anorientation of the tracker 16 in a coordinate system (e.g., of theoptical sensor 14).

The source 22 of electromagnetic radiation shown in FIG. 2A is a lightemitting diode (LED). Alternatively, the source 22 of electromagneticradiation may be any other source capable of emitting electromagneticradiation, such as an organic light emitting diode, a polymer lightemitting diode, a laser, an incandescent light bulb, or a fibre cablecoupled to an emitter of electromagnetic radiation. The source 22 ofelectromagnetic radiation may be configured to emit electromagneticradiation in the visible light spectrum and/or infrared light spectrum.The optical sensor 14 of FIG. 1 is configured to detect at least a partof the spectrum of electromagnetic radiation emitted by the source 22 ofelectromagnetic radiation.

The tracker 16 can be tracked based on one or both of theelectromagnetic radiation 24 emitted by the one or more sources 22 ofelectromagnetic radiation and electromagnetic radiation reflected by oneor more passive tracking elements. As such, the tracker 16 may in someembodiments comprise one or more passive tracking elements configured toreflect electromagnetic radiation. FIG. 3A, B shows a variant of atracker 16 with three passive tracking elements 27A-C. The tracker 16may comprise any other number of passive tracking elements 27, such asone, two, four, or more passive tracking elements 27. The three passivetracking elements 27A-C each comprise a sphere configured to reflectelectromagnetic radiation. The spheres may be configured to reflectpredominantly or entirely a specific light spectrum such as visiblelight, infrared light or ultraviolet light.

The one or more sources 22 of electromagnetic radiation may beconfigured to emit electromagnetic radiation with a light spectrum(e.g., infrared light or visible light) for which the passive trackingelements 27 are reflective (e.g., a reflectance larger than 0.5, 0.7, or0.9). The tracker 16 can therefore be tracked based on electromagneticradiation originating from the sources 22 of electromagnetic radiationand the passive tracking elements 27. Alternatively, the one or moresources 22 of electromagnetic radiation may be configured to emitelectromagnetic radiation with a light spectrum (e.g., infrared light orvisible light) for which the passive tracking elements 27 are not orless reflective (e.g., a reflectance smaller than 0.1, 0.3, or 0.5). Forsuch a tracker 16, reflections of the source 22 of electromagneticradiation by the passive tracking elements 27 that can negatively affecttracking are reduced.

The tracker 16 further comprises a power source 30 configured to providepower to the source 22 of electromagnetic radiation. The power source 30shown in FIGS. 2A is a battery in form of a button cell (e.g., a CR2032or CR2025 button cell). Alternatively, the battery may be a AA or AAAtype cell. A tracker 16 with a smaller battery, such as a button cell,has a smaller weight. A tracker 16 with a larger battery commonly has alarger capacity for a longer operation time. The power source 30 may bea rechargeable battery such as a lithium ion battery. The power source30 may comprise a single battery or a plurality of batteries, such astwo, three, four, or more batteries. Alternatively or additionally, thepower source 30 may comprise a power cord (e.g., to a power socket or anoutlet of a nearby surgical device). In case a wireless power receptiondevice is provided, the tracker 16 will be configured to receive powerwirelessly.

The tracker 16 comprises a first switch 32 configured to be operated bya user between a first switch configuration 34 as shown in FIG. 2A and asecond switch configuration 36 as shown in FIG. 2B.

The source 22 of electromagnetic radiation is configured to selectivelyemit electromagnetic radiation 24 with a first radiation characteristic26 or a second radiation characteristic 28, wherein the first and secondradiation characteristics 26, 28 are different from each other. Thesource 22 of electromagnetic radiation in the state illustrated in FIG.2A (first switch configuration 34) emits electromagnetic radiation 24with the first radiation characteristic 26 and the same source 22 ofelectromagnetic radiation in the state illustrated in FIG. 2B (secondswitch configuration 36) emits electromagnetic radiation 24 with thesecond radiation characteristic 26. In case two or more such sources 22are provided, all of those sources 22 may collectively emit with thesame (first or second) radiation characteristic. In other variants, onlya true subset of one or more such sources 22 collectively emit with thesame (first or second) radiation characteristic, while another truesubset of such sources 22 emits with a radiation characteristic that, insome variants, is different from both the first and the second radiationcharacteristic.

The tracker 16 further comprises electrical circuitry 38 (onlyschematically shown in FIGS. 2A and 2B) configured to selectivelycontrol the source(s) 22 of electromagnetic radiation to emitelectromagnetic radiation 24 having the first radiation characteristic26 in the first switch configuration 34 and to emit electromagneticradiation 24 having the second radiation characteristic 26 in the secondswitch configuration 36.

The first switch 32 shown in FIGS. 2A and 2B is an exemplarymechanically operable switch in form of a sliding switch that remains ina switch configuration after being operated. Therefore, the first switch32 does not change autonomously from the first switch configuration 34to the second switch configuration 36 (or vice versa). After moving thefirst switch 32 into a selected switch configuration, a user can workwith the tracker 16 indefinitely in the selected switch configuration.

The first switch 32 may be spring-biased against an operation direction.As an example, the first switch 32 may alternatively be a push button.Such a push button does not require a sliding sideways movement andrequires less space on a surface of the tracker 16. In such animplementation, the first and second switch configurations 34, 36 can beprovided in two different variations as described in the following.

In the first variation, the push button alternates between the first andsecond switch configurations 34, 36 when being operated, but remains ina switch configuration after operation (commonly referred to as latchingswitch). Such a switch type remains in a switch configurationindefinitely.

In the second variation, the push button is biased towards one switchconfiguration (e.g., the first switch configuration) and only switchesto the other switch configuration (e.g., the second switchconfiguration) for the duration that the user is operating the firstswitch 32 (commonly referred to as “momentary switch”). The user cantherefore perform an input similar to a mouse-click, which requires onlylittle physical interaction with the switch 32.

In a third variation, the push button is biased towards one switchconfiguration (e.g., the first switch configuration) and only switchesto the other switch configuration (e.g., the second switchconfiguration) for a fixed time duration after the switch 32 wasoperated. The fixed time duration can be shorter than a manual input(e.g., shorter than 0.1 s, 10 ms, or 1 ms), which can reduce powerconsumption, or longer (e.g., longer than 0.1 s, 1 s, or 10 s) in orderto ensure detection of the emitted electromagnetic radiation. A fixedtime duration can improve input efficiency.

Furthermore, the operation of the switch 32 may be identified by thefixed duration (in addition to the emitted first or second radiationcharacteristic), which increases input accuracy.

FIGS. 4A-C show another variant of a first switch 32 that comprisesmultiple switch portions at two tracker parts 16A and 16B1 or 16B2 thatare removable from each other. The first switch 32 of FIGS. 4A-Ccomprises a first switch portion 70, wherein the first switch portion 70comprises a first, second and third electrode 72A, 72B, 72C that arepart of the electrical circuitry 38. Those electrodes 72A, 72B, 72C areprovided at a first tracker part 16A that also carries the source 22 ofelectromagnetic radiation.

The first switch 32 further comprises two different second tracker parts16B1 and 16B2 respectively carrying a second switch portion 74configured to be electrically coupled to the first switch portion 70 ofthe first tracker part 16A and a third switch portion 76 configured tobe electrically coupled to the first switch portion 70. The secondswitch portion 74 comprises a first electrical connector 78A and thethird switch portion 76 comprises a second electrical connector 78B.FIG. 4B shows the second switch portion 74 when electrically coupled tothe first switch portion 70. Since the tracker parts 16A and 16B1 or16B2 are removable from each other and carry the first, second and thirdswitch portions 70, 74, 76 respectively, the first, second, and thirdswitch portions 70, 74, 76 are also removable from each other.

The two different second tracker parts 16B1 and 16B2 respectivelycomprise a coupling interface 80A and 80B for coupling the tracker 16 toan object such as patient bone or a surgical instrument (not shown). Thefirst coupling interface 80A exemplarily comprises a clamp that isconfigured to clamp onto a body part of a patient, such as a vertebra ora tibia. The second coupling interface 80B exemplarily comprises a ringwith a biasing screw configured to be coupled to a shaft of a surgicalinstrument. Of course, both coupling interface 80A, 80B could also beconfigured identical.

When the first tracker part 16A is mechanically coupled to the secondtracker part 16B1 and, thus, the first switch portion 70 is electricallycoupled to the second switch portion 74, as can be seen in FIG. 4B, thefirst electrical connector 78A is arranged offset relative to the threeelectrodes 72A, 72B, 72C in such a way that the first electricalconnector 78A only electrically connects the first and second electrode72A, 72B, but not the third electrode 72C. Therefore, the firstelectrical connector 78A closes a portion of the electrical circuitry 38(only shown schematically in FIGS. 4A, B), which results in the firstswitch configuration 34 and consequently emission of electromagneticradiation 24 with the first radiation characteristic 26.

When the first tracker part 16A is mechanically coupled to the secondtracker part 16B2 and, thus, the first switch portion 70 is electricallycoupled to the third switch portion 76, as can be seen in FIG. 4C, thesecond electrical connector 78B is arranged offset relative to the threeelectrodes 72A, 72B, 72C in such a way that the second electricalconnector 78B only electrically connects the second and third electrode72B, 72C, but not the first electrode 72A. Therefore, the secondelectrical connector 78B closes another portion of the electricalcircuitry 38 that is different from the portion of the electricalcircuitry 38 closed by the first electrical connector 78A, which resultsin the second switch configuration 36 and consequently emission ofelectromagnetic radiation 24 with the second radiation characteristic28.

As such, prior to a surgical procedure a user can selectively couple thefirst switch portion 70 (i.e., the first tracker part 16A) with eitherof the second and third switch portion 74, 76 (i.e., the second trackerpart 16B1 or the alternative second tracker part 16B2), which causes thetracker 16 to emit electromagnetic radiation with the first or secondradiation characteristics 26, 28 as explained above. The surgicalnavigation system 10 may have access to an association between therespective object associated with first and second coupling interfaces80A, 80B and the corresponding first and second radiation characteristic26, 28. As such, based on the detected radiation characteristic 26, 28the surgical navigation system 10 can differentiate between the objecttracked when the first tracker part 16A is mechanically coupled to thesecond tracker part 16B1 and the object tracked when the first trackerpart 16A is mechanically coupled to the second tracker part 16B1. Incase two first tracker parts 16A are provided, different objects can betracked simultaneously with the navigation system 10 having a prioriknowledge of the object being tracked.

The two different second tracker parts 16B1 and 16B2 and, thus, thefirst and second switch portions 70, 74 shown in FIGS. 4B, C are twoseparate entities.

Alternatively, the second switch portion 74 and the third switch portion76 are assumed by a single switch portion provided at a single secondtracker part (not shown), wherein the single switch portion “activates”the second switch portion 74 when coupled to the first switch portion 70of the first tracker part 16A for example at a first relative angle(e.g., 0°) and “activates” the third switch portion 76 when coupled tothe first switch portion 70 of the first tracker part 16A for example ata second relative angle different than the first relative angle (e.g.,180°). The difference between the first relative angle and the secondrelative angle can be any angle larger than zero such as 30°, 45°, 90°,120°, and 180°.

The variant of the first switch described above in the context of FIGS.4A-C comprises a plurality of electrodes that are selectively connecteddepending on a position of an electrical connector. Alternatively, thefirst switch portion 70 may only comprise two electrodes that areconfigured to be electrically coupled with the second and third switchportion 74, 76, wherein the second and third switch portions 74, 76differ in electrical characteristics (e.g., an electrical resistance,capacitance, or inductance). For example, the second switch portion 74may be configured to electrically connect the two electrodes of thefirst switch portion 70 with a first electrical resistance assigned tothe first switch configuration 34 and the second switch portion 74 maybe configured to electrically connect the two electrodes with a secondresistance assigned to the second switch configuration 36 and differentfrom the first resistance.

Further alternatively, the second and third switch portions 74, 76 maycomprise a part of the electrical circuitry 38 that is configured tocontrol the one or more sources 22 of electromagnetic radiation to emitelectromagnetic radiation 24 comprising the first or second radiationcharacteristic 26, 28. For example, when the second switch portion 74 iselectrically coupled to the first switch portion 70, electricalcircuitries of the first switch portion 70 and the second switch portion74 form together a combined electrical circuitry configured to controlthe one or more sources 22 of electromagnetic radiation to emitelectromagnetic radiation 24 comprising the first radiationcharacteristic 26. On the other hand, when the third switch portion 76is electrically coupled to the first switch portion 70, electricalcircuitries of the first switch portion 70 and the third switch portion76 form together a combined electrical circuitry configured to controlthe one or more sources 22 of electromagnetic radiation to emitelectromagnetic radiation 24 comprising the second radiationcharacteristic 28.

FIG. 5 shows a flowchart 100 of an embodiment of a method for operatingthe tracker 16.

The method may optionally comprise providing power, in step 102, by apower source 30, to the one or more sources 22 of electromagneticradiation. The method 100 further comprises selectively emitting, instep 104, by the one or more sources 22, electromagnetic radiation 24having the first radiation characteristic 26 in the first switchconfiguration 34 and electromagnetic radiation 24 having the secondradiation characteristic 28 in the second switch configuration 36. Inorder to switch between the first and second radiation characteristics26 and 28, the switch 32 is switched between the first switchconfiguration 34 and the second switch configuration 26 such asdescribed above.

In some variants of the method, the tracker 16 allows the user tocommunicate with the surgical navigation system 10 of FIG. 1. Asmentioned above, the optical sensor 14 is configured to detect theelectromagnetic radiation emitted by the tracker 16. Based on thedetected electromagnetic radiation, the processor 12 (or any othercomputer system communicatively connected with the surgical navigationsystem 10) is configured to selectively identify (e.g., differentiatebetween) the first or second switch configuration 34, 36 based on theradiation characteristic detected by the optical sensor 14. Theprocessor 12 may have access to information on the first and secondradiation characteristics (such as an operation frequency, wavelength,or geometric arrangement of sources 22 as will be described furtherbelow) that allow identifying the switch configuration 34, 36 from theactually detected radiation characteristics. The information may beprovided to the processor 12 during manufacturing, maintenance orcalibration. The information may be provided in form of one or morepredetermined radiation characteristics. As such, the processor 12 maybe configured to identify the first or second switch configuration 34,36 by comparing the detected radiation characteristic with the one ormore predetermined radiation characteristics.

The processor 12 may in particular be configured to assign a firsttracking mode to the first switch configuration 34 and a second trackingmode to the second switch configuration 36. The first and secondtracking modes can be associated with different surgical objects (suchas a body part of a patient and an instrument) that the tracker 16 iscoupled to. For example, the first tracking mode may be associated totracking a patient and the second tracking mode may be associated withtracking an instrument.

Alternatively, the first and second tracking mode may be associated withdifferent body parts of the patient. For example, the first trackingmode may be associated with a tibia of a patient and the second mode maybe associated with a femur of a patient. In such a case, the user cancouple the tracker 16 to the tibia and operate the first switch 32 ofthe first tracker 16 to switch into the first switch configuration 34.In some implementations, the user can additionally couple a secondtracker 16 to the femur of the patient and operate the first switch 32of the second tracker 16 to switch into the second switch configuration36. The processor 12 can identify the tracking mode of the respectivetracker 16 based on the respective radiation characteristics. Theprocessor 12 may determine based on the identified tracking mode(s) thatthe first tracker 16 is coupled to the tibia (and, if present, that thesecond tracker 16 is couple to the femur).

In case a plurality of sources 22 of electromagnetic radiation areprovided at a given tracker 16, the processor 12 may determine aposition and/or orientation of that tracker 16 and, based thereon, ofthe surgical object to be tracked by that tracker 16. As an example, heprocessor 12 may process (e.g., calibrate or visualize) image data ofthe tibia and/or the femur dependent on a detected position and/ororientation of the respective tracker 16. By setting up the switchconfigurations of the first and second trackers 16, the user effectivelyis able to communicate with the processor 12, without having to use amechanically operated input device of the computer system 18, such as akeyboard or mouse.

The possibilities of the user to communicate with the surgicalnavigation system 10 are not limited to selecting a certain switchconfiguration (e.g., pre-operatively). The user may communicate with thesurgical navigation system 10 by switching the switch configuration(e.g., during a surgical procedure). To this end, the processor 12 maybe configured to specifically identify a switching between the first andsecond switch configuration 34, 36. The processor 12 may, for example,identify the switching between the first and second switch configuration34, 36 as a command issued by the user. The command may be related tosurgical navigation. For example, the user may switch between the firstand second switch configuration 34, 36 in order to instruct the surgicalnavigation system 10 to perform a certain processing step (e.g., tochange a visual representation on a display). The instruction mayalternatively be related to other aspects of the surgery such asoperation of a surgical instrument (to which the tracker 16 may or maynot be attached). For issuing a command, the first switch 32 may be apush button that is biased towards one switch configuration and thatonly switches to the other switch configuration for the duration theuser is operating the first switch 32. For example, the surgicalnavigation system 10 may activate a suction tube for the duration thesurgeon is operating the first switch 32.

It should be noted that the tracker 16 is not limited to providing onlytwo switch configurations. The tracker 16 may have a first switch 32with three, four, five, six, or more switch configurations. FIGS. 6A-Cshow a variant of the first switch 32 that has three switchconfigurations, wherein the first switch configuration (in FIGS. 6A-Cthe left position of the first switch 32) is assigned to the firstradiation characteristic 34 and the second switch configurations (inFIGS. 6A-C the middle position of the first switch 32) is assigned tothe second radiation characteristics 28. A third switch configuration(in FIGS. 6A-C the right position of the first switch 32) allows theuser to switch off the tracker 16. Alternatively, the tracker 16 mayhave a separate power switch for switching the tracker 16 on and off.The tracker 16 may be a disposable item, wherein the power switch isoperable exactly once to switch on the tracker 16. In such a case, theswitch may be switched on by removing a removable isolating materialthat interrupts a portion of the electrical circuitry 38.

Furthermore, the source 22 of electromagnetic radiation is not limitedto selectively assuming a first and second radiation characteristic 26,28. Alternatively, the source 22 of electromagnetic radiation may beconfigured to selectively emit electromagnetic radiation with more thantwo radiation characteristics 26, 28, such as three, four, five, six, ormore radiation characteristics. In such a case, the first switch 32 mayhave a plurality of switch configurations, wherein each switchconfiguration is assigned to one of the plurality of radiationcharacteristics. FIGS. 6D-F show an embodiment of a tracker 16, whereinthe source 22 of electromagnetic radiation may be configured toselectively emit electromagnetic radiation with three differentradiation characteristics and the first switch 32 has three switchconfigurations, one for each of the three radiation characteristic (andoptionally, a fourth switch configuration for switching the tracker 16on or off).

As will be described further below, a change between the first andsecond radiation characteristics 24, 26 may not be visible to the user.However, the first and second radiation characteristics 24, 26 arelinked to the first and second switch configurations 34, 36. In order toallow the user to easier distinguish between the first and secondradiation characteristic 24, 26, the tracker 16 may comprise anindicator configured to provide a first indication to the user in thefirst switch configuration 34 and a second indication to the user in thesecond switch configuration 36, wherein the first and second indicationsare at least one of optically and haptically distinguishable for theuser. The user can then identify the first and second radiationcharacteristics 24, 26 by identifying the related first and secondswitch configurations 34, 36.

In this regard, FIGS. 7A and 7B show a tracker 16 similar to the one ofFIGS. 2A and 2B, but with a plurality of indicators 48A, 48B, 48C, 48Dconfigured to provide a first indication in the first switchconfiguration 34 and a second indication in the second switchconfiguration 36. In detail, FIG. 7A shows the tracker 16 assuming thefirst switch configuration 34 and FIG. 7B shows the tracker 16 assumingthe second switch configuration 36. FIGS. 7A and 7B show a combinationof indicators 48 for the sake of a concise depiction of the indicators48. However, it should be understood that the tracker 16 may have onlyone indicator 48 or any combination of indicators 48 described herein.

The tracker 16 shown in FIGS. 7A and 7B comprises an indicator lightsource 48A configured to emit visible light perceivable by the humaneye. The indicator light source 48A is configured to emit light with afirst visible wavelength (e.g., a green light) in the first switchconfiguration 34 and emit light with a second visible wave-length (e.g.,a red light) in the second switch configuration 36. Alternatively, theindicator light source 48A may be configured to emit light with avisible wavelength in one of the first and second switch configuration34, 36 and to emit no light in the other one of the first and secondswitch configuration 34, 36. Alternatively or additionally, theindicator light source 48A may be configured to operate in a thirdoperation frequency perceivable by the human eye (e.g., 2 Hz) in thefirst switch configuration and in a fourth operation frequencyperceivable by the human eye (e.g., 6 Hz) in the second switchconfiguration.

The tracker 16 shown in FIGS. 7A and 7B comprises as a further oralternative indicator 48 a first switch position indicator 48Bconfigured to assign a first position of the first switch 32 to thefirst switch configuration 34 and to assign a second position of thefirst switch 32 to the second switch configuration 36. The first switchposition indicator 48B shown in FIGS. 7A and 7B comprises a numbering inRoman numerals. Alternatively, the first switch position indicator 48Bmay comprise different symbols and/or terms (e.g., describing differenttracking modes). For example, the first switch position indicator 48Bmay comprise terms that indicate whether the tracker 16 is coupled to aninstrument or a patient (e.g., with the terms “instrument” and“patient”, or “I” and “P”). Further alternatively, the first switchposition indicator 48B may comprise terms that indicate anatomical partsof the patient that the tracker 16 is coupled to (e.g., with the terms“tibia” and “femur”, or “T” and “F”). The first switch positionindicator 48B may be formed raised or recessed relative to a surroundingregion of the tracker 16 in order to be haptically distinguishable forthe user.

The tracker 16 shown in FIGS. 7A and 7B comprises as a further oralternative indicator 48 a second switch position indicator 48Cconfigured to display a first symbol in the first switch configuration34 and a second symbol in the second switch configuration 36. In theexample shown in FIGS. 7A and 7B, the first symbol is a white square andthe second symbol is a black square. Alternatively, the first and secondsymbol may be any other set of symbols that are opticallydistinguishable for the user. The first switch 32 covers the secondsymbol in the first switch configuration 34 and uncovers the secondsymbol in the second switch configuration 36. Similarly, the firstsymbol is covered by the first switch 32 in the second switchconfiguration 36 and uncovered in the first switch configuration.Therefore, the first symbol is visible to the user in the first switchconfiguration 34 and the second symbol is visible to the user in thesecond switch configuration 36. Evidently, one of the two symbols may beomitted, so that only a single symbol, when being uncovered, providesdiscrete visual feedback to the user.

The tracker 16 shown in FIGS. 7A and 7B comprises as a still further oralternative indicator 48 a haptic switch feature 48D. The haptic switchfeature 48D enables the user an easier operation of the first switch 32and allows the user to haptically determine the switch configuration ofthe first switch 32 (e.g., with reference to another haptic feature thatremains stationary).

In the following, different embodiments of specific radiationcharacteristics are described. The different radiation characteristicsare not exclusive to each other and may therefore be combined in anycombination.

In one example, the first radiation characteristic 26 comprises emissionof electromagnetic radiation 24 at a first operation frequency and thesecond radiation characteristic 28 comprises emission of electromagneticradiation at a second operation frequency different from the firstoperation frequency. The first and second operation frequencies eachindicate a rate of a periodic intensity change of the electromagneticradiation 24. The frequencies and rates may be visually distinguishable(e.g., be selected to fall within a range of 0,5 Hz to 20 Hz, or tocorrespond to a continuous radiation emission)

FIG. 8A shows in a time diagram an intensity change of theelectromagnetic radiation 24 at a first operation frequency. As can beseen, the intensity periodically alternates between a higher intensityand a lower intensity. The operation frequency may be defined by a timeduration between two points of time at which the intensity switches fromthe lower intensity to the higher intensity.

The lower intensity shown in FIG. 8A is larger than zero. Alternatively,the lower intensity can be zero (or essentially zero). FIG. 8B shows ina time diagram an intensity change of the electromagnetic radiation 24at the first operation frequency, wherein the intensity alternatesbetween an intensity of zero and an intensity that is larger than zero.A source 22 of electromagnetic radiation operating at such an operationfrequency alternates between emitting light and not emitting light atthe operation frequency.

FIG. 8C shows in a time diagram a change of the intensity of theelectromagnetic radiation 24 from the first operation frequency 40 to asecond operation frequency.

In the example shown in FIG. 8C, the first operation frequency 40 issmaller than the second operation frequency 42. Alternatively, the firstoperation frequency 40 may be higher than the second operation frequency42.

The change of the operation frequency can be caused by the userswitching the switch configuration as described in the following.Initially, the switch 32 is set in the first switch configuration 34(see, e.g., FIG. 2A). The electrical circuitry 38 is con- figured toselectively control the (at least one) source 22 of electromagneticradiation to emit electromagnetic radiation 24 at the first operationfrequency 40 in the first switch configuration 34. The user thenoperates the switch 32 to switch from the first switch configuration 34to the second switch configuration 36 (see, e.g., FIG. 2B). Thereupon,the electrical circuitry 38 is configured to selectively control the (atleast one) source 22 of electromagnetic radiation to emitelectromagnetic radiation 24 having the second operation frequency 42.

FIG. 8C shows a single change of the radiation characteristic. Such achange may be signalled with a switch 32 that permanently remains in thesecond switch con- figuration 36, such as the one explained above. Theuser can subsequently use the tracker 16 while the at least one source22 of electromagnetic radiation emits electromagnetic radiation 24 withthe second radiation characteristic, i.e., at the second operationfrequency 42.

The radiation characteristic may be changed multiple times, such astwice, thrice or, four times during a surgical procedure. The timediagram of FIG. 8D shows a first change 44 of the intensity of theelectromagnetic radiation 24 from the first operation frequency 40 tothe second operation frequency 42 followed by a second change 46 back tothe first operation frequency 40. In essence, the radiationcharacteristic 24 initially comprises the first operation frequency 40and temporally switches to the second operation frequency 42.

The change of the radiation characteristic 24 may be performed with aswitch 32 that permanently remains in a switch configuration after beingoperated such as the one shown in FIG. 2A. Alternatively, the radiationcharacteristic 24 may be changed using a switch 32 that only temporarilyswitches to the second switch configuration for the duration the user isoperating the switch 32 (or for a fixed time duration after the switch32 was operated by the user).

The second operation frequency 42 shown in FIGS. 8C and 8D is anoperation frequency that is larger than zero. Alternatively, the secondoperation frequency 42 (or the first operation frequency 40) may be zero(or, conversely, infinite), corresponding to a continuous emission ofelectromagnetic radiation 24. The intensity of electromagnetic radiation24 during the continuous emission may be equal to the larger intensityof the first operation frequency 40 as shown in FIG. 8E. Alternatively,the intensity may be smaller in order to reduce power consumption.

The optical sensor 14 discussed above with reference to FIG. 1 (such asthe camera described above) may have a frame rate that is larger (e.g.,two times or three times larger) than a larger one of the first andsecond operation frequencies 40, 42 of the tracker 16. An optical sensor14 having such a frame rate has a better probability of properlyresolving the first and second operation frequencies 40, 42 and,therefore, increases the accuracy of the surgical navigation system 10.

As explained above, one way the first and second radiationcharacteristics 26, 28 may differ is in the operation frequency.Additionally or alternatively, the first radiation characteristic 26 maycomprise emission of electromagnetic radiation having a first wavelengthand the second radiation characteristic 28 comprises emission ofelectromagnetic radiation having a second wavelength different from thefirst wavelength. The first wavelength and the second wavelength may bewithin the visible spectrum (e.g., red and green or white and blue). Theuser can then easily differentiate between the first and secondradiation characteristics 26, 28 based on the colour of the lightemitted by the at least one source 22 of electromagnetic radiation.Alternatively, the first and second wavelengths may be outside thevisible spectrum, such as in the infrared spectrum. Such a tracker 16 isless distracting to the user and less affected by ambient lighting.

The tracker 16 shown in FIG. 2A only comprises a single source 22 ofelectromagnetic radiation 24. However, as said, the tracker 16 is notlimited to a single source 22 of electromagnetic radiation.Alternatively, the tracker 16 may comprise a plurality of sources 22 ofelectromagnetic radiation such as two, three, four, five, six, or moresources 22 of electromagnetic radiation. The electrical circuitry 38 maybe configured to selectively control the plurality of sources 22 ofelectromagnetic radiation in unison to emit electromagnetic radiation 24having the first radiation characteristic 26 in the first switchconfiguration 34 and to emit electromagnetic radiation 24 having thesecond radiation characteristic 28 in the second switch configuration36. For example, when the first switch 32 switches from the first switchconfiguration 34 to the second switch configuration 36, all sources 22of electromagnetic radiation emit light at the second operationfrequency 42 and/or the second wavelength.

Alternatively or additionally, changing between the first and secondradiation characteristics 26, 28 of the plurality of sources 22 ofelectromagnetic radiation may comprise at least one of (i) at least oneof the sources 22 of electromagnetic radiation starting emittingelectromagnetic radiation 24 and (ii) at least one of the sources 22 ofelectromagnetic radiation stopping emitting electromagnetic radiation24.

FIGS. 9A and 9B show an embodiment of a tracker 16 with multiple (here:three) sources 22 of electromagnetic radiation that can be controlledindividually or in sets to stop, continue, or start emittingelectromagnetic radiation 24. That is, the tracker 16 comprises a firstsource 22A, a second source 22B, and a third source 22C ofelectromagnetic radiation (and, optionally, a fourth source). As can beseen in FIG. 9A, when the first switch 32 is in the first switchconfiguration 34, the electrical circuitry 38 is configured toselectively control the plurality of sources 22 of electromagneticradiation to emit electromagnetic radiation 24 having the firstradiation characteristic 26, wherein the first radiation characteristic26 comprises the first and second sources 22A, 22B of electromagneticradiation emitting electromagnetic radiation and the third source 22C ofelectromagnetic radiation not emitting electromagnetic radiation.

As can be seen in FIG. 9B, once the first switch 32 switches from thefirst switch configuration 34 to the second switch configuration 36, theelectrical circuitry 38 is configured to selectively control theplurality of sources 22 of electromagnetic radiation to emitelectromagnetic radiation 24 having the second radiation characteristic26, wherein the first source 22A of electromagnetic radiation stopsemitting electromagnetic radiation, the second source 22B ofelectromagnetic radiation continues emitting electromagnetic radiation,and the third source 22C of electromagnetic radiation stops emittingelectromagnetic radiation.

The second source 22B of electromagnetic radiation is spaced furtherapart from the third source 22C of electromagnetic radiation than fromthe first source 22A of electromagnetic radiation. The two sources 22B,22C emitting electromagnetic radiation in the second radiationcharacteristic 28 are arranged in a different orientation and distancerelative to each other compared to the two sources 22A, 22B emittingelectromagnetic radiation in the first radiation characteristic 26.Therefore, the second radiation characteristic 26 differs geometricallyfrom the first radiation characteristic 24. By operating the firstswitch 32, the user can effectively change a geometrical pattern ofsources 22 of electromagnetic radiation that emit electromagneticradiation 24.

In some variants, a fourth or fifth source 22 of electromagneticradiation may be provided. The plurality of sources 22 ofelectromagnetic radiation may then be controlled such that at least(e.g., exactly) three sources 22 of electromagnetic radiation areemitting with the same radiation characteristic 26, 28 (e.g., aresimultaneously on) in each switch configuration 34, 36.

FIGS. 10A and 10B show another variant of a tracker 16 comprising eightsources 22 of electromagnetic radiation. In the first switchconfiguration 34 shown in FIG. 10A, three sources 22 of electromagneticradiation emit electromagnetic radiation 24 (which is denoted in FIG.10A as white filled circles). Five sources 22 of electromagneticradiation do not emit electromagnetic radiation 24 (which is denoted inFIG. 10A with black filled circles). The tracker 16 has a lower powerconsumption while in the first switch configuration 34.

In the second switch configuration 36 shown in FIG. 10B, all eightsources 22 of electromagnetic radiation emit electromagnetic radiation24. A position and/or orientation of the tracker 16 can be determinedmore accurately by the surgical navigation system 10 while the tracker16 is in the second switch configuration 36.

The trackers 16 described above comprise one switch 32. However, thetracker 16 is not limited to a single switch 32. Alternatively, thetracker 16 may comprise a plurality of switches.

FIGS. 11A to 11D show a variant of a tracker 16 with a plurality ofsources 22 of electromagnetic radiation, a first switch 32 and a secondswitch 50. The tracker 16 has six sources 22A-F of electromagneticradiation. A first subset 52 comprises a first and second source 22A,22B of electromagnetic radiation that is assigned to the first switch32. A second subset 54 comprises a third and fourth source 22C, 22D ofelectromagnetic radiation that is assigned to the second switch 50.

The switch 32 is configured to be operated by the user between a firstswitch configuration (shown in FIGS. 11A and 11C) and a second switchconfiguration (shown in FIGS. 11B and 11D). The further switch 50 isconfigured to be operated by the user between a third switchconfiguration (shown in FIGS. 11A and 11B) and a fourth switchconfiguration (shown in FIGS. 11C and 11D).

The first subset 52 of the plurality of sources 22 of electromagneticradiation is configured to selectively emit electromagnetic radiation 24having a first partial radiation characteristic or a second partialradiation characteristic. The first partial radiation characteristiccomprises the first source 22A of electromagnetic radiation emittingelectromagnetic radiation and the second source 22B of electromagneticradiation not emitting electromagnetic radiation, as shown in FIGS. 11Aand 11C. The second partial radiation characteristic comprises the firstsource 22A of electromagnetic radiation not emitting electromagneticradiation and the second source 22B of electromagnetic radiationemitting electromagnetic radiation, as shown in FIG. 11B. In essence,the first and second partial radiation characteristics differ in whetherthe first source 22A or the second source 22B is emittingelectromagnetic radiation.

The second subset 54 of the plurality of sources 22 of electromagneticradiation is configured to selectively emit electromagnetic radiation 24having a third partial radiation characteristic or a fourth partialradiation characteristic. The third partial radiation characteristiccomprises the third source 22C of electromagnetic radiation emittingelectromagnetic radiation and the fourth source 22D of electromagneticradiation not emitting electromagnetic radiation, as shown in FIG. 11A.The fourth partial radiation characteristic comprises the third source22C of electromagnetic radiation not emitting electromagnetic radiationand the fourth source 22D of electromagnetic radiation emittingelectromagnetic radiation as shown in FIG. 11C. Again, the third andfourth partial radiation characteristic differ in whether the thirdsource 22C or fourth source 22D is emitting electromagnetic radiation.

The two switches 32, 50 are configured to be operated by the user toonly change the partial radiation characteristic of each assigned subset52, 54 of sources 22A-D of electromagnetic radiation. Therefore, theuser can operate the first switch 32 in order to change the partialradiation characteristic of the first subset 52 without changing thepartial radiation characteristic of the second subset 52. Vice versa,the user can operate the second switch 50 in order to change the partialradiation characteristic of the second subset 54 without changing thepartial radiation characteristic of the first subset 52.

The radiation characteristic 24 of the entire tracker 16 comprises thepartial radiation characteristic of each subset 52, 54. Since eachsubset 52, 54 can switch between two partial radiation characteristics,the tracker 16 has four radiation characteristics that are shown inFIGS. 11A-D. FIG. 11A shows the tracker 16 with a first radiationcharacteristics comprising the first partial radiation characteristic ofthe first subset 52 and the third partial radiation characteristic ofthe second subset 54. FIG. 11B shows the tracker 16 with a secondradiation characteristics comprising the second partial radiationcharacteristic of the first subset 52 and the third partial radiationcharacteristic of the second subset 54. FIG. 11C shows the tracker 16with a third radiation characteristics comprising the first partialradiation characteristic of the first subset 52 and the fourth partialradiation characteristic of the second subset 54. FIG. 11D shows thetracker 16 with a fourth radiation characteristics comprising the secondpartial radiation characteristic of the first subset 52 and the fourthpartial radiation characteristic of the second subset 54.

The sources of radiation 22E and 22F may in some variants be included inthe first subset 52, and the second subset 54, respectively. In somevariants, the sources 22E and 22F can be omitted.

The tracker 16 shown in FIGS. 11A-D comprises two subsets of sources 22of electromagnetic radiation. Alternatively, the tracker 16 may comprisemore than two subsets of sources 22 of electromagnetic radiation. FIG.12A shows a tracker 16 with four subsets 52, 54, 56, 58 of sources 22 ofelectromagnetic radiation and four switches 32, 50, 60, 62. Each switch32, 50, 60, 62 is assigned to one of the four subsets 52, 54, 56, 58 andallows switching between two partial radiation characteristics of eachassigned subset 52, 54, 56, 58. The radiation characteristic 24 of theentire tracker 16 comprises the partial radiation characteristic of eachsubset 52, 54, 60, 62 and, therefore, comprises sixteen differentradiation characteristics.

The subsets of the trackers 16 shown in FIGS. 11A-D and 12A eachcomprise exactly two sources 22 of electromagnetic radiation, whereineach subset can change between two different partial radiationcharacteristics. Alternatively, the tracker 16 may comprise subsets withmore than two (e.g., three, four or more) sources 22 of electromagneticradiation and/or subsets each with more than two (e.g., three, four ormore) different partial radiation characteristics. FIG. 12B shows avariant of a tracker 16 with four subsets 52, 54, 56, 58 each with fourof sources 22 of electromagnetic radiation, and four switches 32, 50,60, 62 each assigned to one of the corresponding subsets 52, 54, 56, 58.Furthermore, each switch 32, 50, 60, 62 has four switch configurationsthat allows selecting one source 22 of electromagnetic radiation of theassigned subsets 52, 54, 56, 58 to emit electromagnetic radiation.

For the subsets described above, each partial radiation characteristiccomprises exactly one source 22 of electromagnetic radiation emittingelectromagnetic radiation, while the remaining sources 22 ofelectromagnetic radiation of the subset do not emit electromagneticradiation. Therefore, changing the partial radiation characteristicessentially changes which single source 22 of the subset is emittingelectromagnetic radiation. However, a partial radiation characteristicmay not only comprise a single source 22 of electromagnetic radiationemitting electromagnetic radiation. A partial radiation characteristicmay comprise multiple (e.g., three, four or more) sources 22 of theassociated subset emitting electromagnetic radiation.

Consequently, changing a partial radiation characteristic may comprise aplurality of sources 22 of the associated subset stopping or continuingto emit electromagnetic radiation.

It is noted that the sources 22 of electromagnetic radiation for thetrackers 16 shown in FIGS. 10 and 11 are preferably arrangedasymmetrically in order to prevent a ambiguous orientations and/orpositions of the trackers 16 while tracking. Furthermore, the sources 22of electromagnetic radiation are preferably arranged in such a way thatany geometrical arrangement of the sources 22 of electromagneticradiation that can be the result of different switch configurations isalso asymmetrical. The sources 22 of electromagnetic radiation may alsobe arranged in such a way that any geometrical arrangement of thesources 22 of electromagnetic radiation that can be the result ofdifferent switch configurations is unique.

The features described in relation to the exemplary embodiments shown inthe drawings can be readily combined to result in different embodiments.It is apparent, therefore, that the present disclosure may be varied inmany ways. Such variations are not to be regarded as a departure fromthe scope of the invention as defined by the claims appended hereto.

1. A tracker for a surgical navigation system, the tracker comprising: afirst switch configured to be operated between a first switchconfiguration and a second switch configuration; one or more sources ofelectromagnetic radiation configured to selectively emit electromagneticradiation with a first radiation characteristic or a second radiationcharacteristic; and electrical circuitry configured to selectivelycontrol the one or more sources of electromagnetic radiation to emitelectromagnetic radiation having the first radiation characteristic inthe first switch configuration and to emit electromagnetic radiationhaving the second radiation characteristic in the second switchconfiguration, wherein the second radiation characteristic is differentfrom the first radiation characteristic.
 2. The tracker according toclaim 1, wherein the first radiation characteristic comprises emissionof electromagnetic radiation at a first operation frequency and thesecond radiation characteristic comprises emission of electromagneticradiation at a second operation frequency different from the firstoperation frequency, wherein the first and second operation frequencieseach indicate a rate of a periodic intensity change of theelectromagnetic radiation.
 3. The tracker according to claim 2, whereinone of the first operation frequency and the second operation frequencyis zero with a continuous emission of electromagnetic radiation.
 4. Thetracker according to claim 1, wherein the first radiation characteristiccomprises emission of electromagnetic radiation having a firstwavelength and the second radiation characteristic comprises emission ofelectromagnetic radiation having a second wavelength different from thefirst wavelength.
 5. The tracker according to claim 1, wherein thetracker comprises a plurality of sources of electromagnetic radiation,and wherein changing between the first and second radiationcharacteristics of the plurality of sources of electromagnetic radiationcomprises at least one of: at least one of the sources ofelectromagnetic radiation starting emitting electromagnetic radiation;and at least one of the sources of electromagnetic radiation stoppingemitting electromagnetic radiation.
 6. The tracker according to claim 5,wherein a first subset of sources of electromagnetic radiation comprisesexactly two sources of electromagnetic radiation, and wherein in thefirst radiation characteristic only one source of the first subset isconfigured to emit electromagnetic radiation, and in the secondradiation characteristic only the other source of the first subset isconfigured to emit electromagnetic radiation.
 7. The tracker accordingto claim 5, further comprising a second switch configured to be operatedbetween a third switch configuration and a fourth switch configuration,wherein a first subset of the plurality of sources of electromagneticradiation is assigned to the first switch and a second subset of theplurality of sources of electromagnetic radiation is assigned to thesecond switch, wherein the first subset of the plurality of sources ofelectromagnetic radiation is configured to selectively emitelectromagnetic radiation having a first partial radiationcharacteristic or a second partial radiation characteristic, wherein thesecond subset of the plurality of sources of electromagnetic radiationis configured to selectively emit electromagnetic radiation having athird partial radiation characteristic or a fourth partial radiationcharacteristic, and wherein the first and second switches are configuredto be operated to only change the partial radiation characteristic ofeach assigned subset of the plurality of sources of electromagneticradiation.
 8. The tracker according to claim 1, further comprising anindicator configured to provide a first indication in the first switchconfiguration and a second indication in the second switchconfiguration, wherein the first and second indications are at least oneof optically and haptically distinguishable for a user.
 9. The trackeraccording to claim 1, wherein the first switch is preconfigured toassume the first switch configuration and adapted to switch from thefirst to the second switch configuration only for a duration that thefirst switch is operated or for a fixed time duration after the firstswitch was operated.
 10. The tracker according to claim 1, furthercomprising one of a power source and a wireless power reception device.11. The tracker according to claim 1, further comprising one or morepassive tracking elements configured to reflect electromagneticradiation.
 12. The tracker according to claim 1, wherein the firstswitch has more than two switch configurations, and wherein the one ormore sources of electromagnetic radiation are configured to selectivelyemit electromagnetic radiation with a number of radiationcharacteristics at least equal to a number of switch configurations,wherein each of the switch configurations is assigned to one of theradiation characteristics.
 13. The tracker according to claim 1, whereinthe first switch comprises a mechanical switch configured to be operatedby a user.
 14. The tracker according to claim 1, wherein the firstswitch comprises: a first switch portion; a second switch portionconfigured to be electrically coupled to the first switch portion; and athird switch portion configured to be electrically coupled to the firstswitch portion, wherein the first switch is in the first switchconfiguration when the second switch portion is electrically coupled tothe first switch portion and in the second switch configuration when thethird switch portion is electrically coupled to the first switchportion.
 15. The tracker according to claim 14, wherein the trackercomprises a first tracker part and at least one second tracker part thatis one of movable relative to and removable from the first tracker part,and wherein the first switch portion is provided at the first trackerpart and the second switch portion and the third switch portion arecollectively or individually provided at the at least one second trackerpart.
 16. The tracker according to claim 15, wherein one of the firstand the at least one second tracker part carries the one or more sourcesof electromagnetic radiation, and wherein the other of the first and theat least one second tracker part comprises an interface for coupling thetracker to an object that is to be tracked.
 17. A surgical navigationsystem comprising: a tracker comprising a first switch configured to beoperated between a first switch configuration and a second switchconfiguration, the tracker further comprising one or more sources ofelectromagnetic radiation configured to selectively emit electromagneticradiation with a first radiation characteristic or a second radiationcharacteristic, and electrical circuitry configured to selectivelycontrol the one or more sources of electromagnetic radiation to emitelectromagnetic radiation having the first radiation characteristic inthe first switch configuration and to emit electromagnetic radiationhaving the second radiation characteristic in the second switchconfiguration, wherein the second radiation characteristic is differentfrom the first radiation characteristic; an optical sensor capable ofdetecting different radiation characteristics of the tracker; and aprocessor configured to selectively identify the first or second switchconfiguration based on the radiation characteristic detected by theoptical sensor.
 18. The surgical navigation system according to claim17, wherein the processor is configured to assign a first tracking modeto the first switch configuration and a second tracking mode to thesecond switch configuration.
 19. The surgical navigation systemaccording to claim 17, wherein: the first radiation characteristiccomprises emission of electromagnetic radiation at a first operationfrequency and the second radiation characteristic comprises emission ofelectromagnetic radiation at a second operation frequency different fromthe first operation frequency, the first and second operationfrequencies each indicate a rate of a periodic intensity change of theelectromagnetic radiation, and the optical sensor is a camera having aframe rate that is at least two times larger than a larger one of thefirst and second operation frequencies of the tracker.
 20. A method foroperating a tracker for a surgical navigation system, the trackercomprising a first switch configured to be operated between a firstswitch configuration and a second switch configuration, one or moresources of electromagnetic radiation, and electrical circuitryconfigured to selectively control the one or more sources ofelectromagnetic radiation to emit electromagnetic radiation with a firstradiation characteristic or a second radiation characteristic, whereinthe second radiation characteristic is different from the firstradiation characteristic, wherein the method comprises: emitting, by theone or more sources of electromagnetic radiation, electromagneticradiation having the first radiation characteristic in the first switchconfiguration and electromagnetic radiation having the second radiationcharacteristic in the second switch configuration.